The number of times ive been out and not turned a reel, either on charter or not, is depressing. Realistically you can't blame the charter guys for giving it a shot for you - average weather or not - although i agree you should have been made aware of the weather conditions prior to passing the heads.
Expecting charter operators to offer discounts for poor fishing is a tough one as consunables such as fuel, bait, tackle etc have been used and need to be replaced, fish or no fish. I can assure you when you own the boat/gear the costs for such a trip exceeds the charter cost you paid and you shouldn't let this experience deter you from having another crack at it.